Multi beam scanning with bright/dark field imaging

ABSTRACT

Bright and dark field imaging operations in an optical inspection system occur along substantially the same optical path using the same light source by producing either a circular or an annular laser beam. Multiple beam splitting is achieved through the use of a diffractive optical element having uniform diffraction efficiency. A confocal arrangement for bright field and dark field imaging can be applied with multiple beam scanning for suppressing the signal from under-layers. A scan direction not perpendicular to the direction of movement of a target provides for improved die-to-die comparisons.

BACKGROUND

[0001] The invention relates to the field of optical inspection systemsfor inspecting semiconductor wafers, and more particularly to inspectingsemiconductor wafers using a scanned beam of laser light.

[0002] Although the title of this description indicates multi beamscanning, it will be appreciated that the advances mentioned in some ofthe embodiments described below relate also to single beam scanning.

[0003]FIG. 1 shows a semiconductor wafer 10. Optical inspection systemsare often used to inspect dies 20 on the semiconductor wafer 10. FIG. 2shows several of the dies 20 of semiconductor wafer 10. Although it iscertainly possible, and very common to compare the pattern of conductorsof a die 20 with a reference image, it is also common for the comparisonto be a die-to-die comparison. That is to say, a die 20 is compared withanother die 20 instead of a reference image. For example, in adie-to-die comparison, dies adjacent to each other could be compared,such as the top to dies shown in the figure. Likewise, instead ofcomparing a die to another die in the same row, a comparison could bemade between one die and another in the same column.

[0004]FIG. 3 shows a beam of light 100 being made to impinge upon thesurface of the die 20. The main optical scanning direction is indicatedby the letter O. The mechanical scanning direction is indicated by theletter M. The mechanical scanning direction is the direction in whichthe stage moves the wafer, and also may be referred to as the directionof movement of the wafer or the target movement direction.

[0005]FIG. 4 shows a system that employs dark field imaging. In FIG. 4,the wafer 10 is mounted on the X-Y stage 12. A light source 200 produceslight which is shaped, focused, or operated on as necessary by optics210 and provided to a scanner 300. The scanner 300 outputs the light insuch a manner that, after passing through optics 310, follows a scanpattern across the die 20 on the wafer 10. The scanner can beimplemented by a rotating polygon, deflection mirror, or acoustic-opticsdeflector (AOD). As is well known, dark field imaging uses detectors 410positioned so as to capture light 110 that is scattered rather thenreflected off of the surface of the die.

[0006]FIG. 5 shows a system that employs bright field imaging. In brightfield imaging, the reflected light 120 is captured by a detector 420.The detector can be a PIN diode, PMT, or line CCD camera. The optics310, in this case, could include e.g. a beam splitter. Thus, light fromthe light source 200 travels through beam shaper 205 and optics 210, andis caused by the scanner 300 to impinge on the surface of the die 20 onwafer 10, and the reflected light 120 is channeled back through theoptics 310 to the bright field detector 420.

[0007] To put it another way, the bright field optical inspection systemcollects the specularly reflected light, whereas the dark field systemcollects the scattered light. Usually, a bright field system is usedwith very high-resolution imaging optics, and the inspection of thewafer is performed in such a manner that the pixel size is very small.The small pixel size makes maximum advantage of the high-resolutionimaging optics and the large amount of reflected light. Bright fieldsystems thus provide a great deal of detail, and are excellent when suchdetail is necessary.

[0008] Dark field systems provide a much higher throughput. Dark fieldsystems typically use laser scan technology for illumination, but theinspection of the wafer is usually performed in such a manner that thepixel size is relatively large. The use of scattered light detection isadvantageous in that it has a high signal to noise ratio and evenrelatively small defects can be detected with high throughput. As willbe understood, higher throughput can be obtained with relatively lower,data rate.

[0009] It will also be appreciated that the systems of FIGS. 4 and 5could be combined, resulting in a system having both bright fielddetectors and dark field detectors, positioned appropriately so that thescattered light can be detected by the dark field detectors and thereflected light can be detected by the bright field detectors asaccomplished in Applied Materials wafer inspection tool, Compass™. It isimportant to notice that in such a configuration the high throughput isobtained by a scanning spot with a relatively large pixel, so theresolution of the BF detector is relatively poor.

[0010] What is needed is a better approach that provides higherthroughput with also high resolution in bright field mode.

SUMMARY OF THE INVENTION

[0011] In one aspect, the invention provides for an improved inspectionmethod and system in which a laser beam having a ring, or annular, shapeis used.

[0012] In another aspect, the invention provides for an improvedinspection method and system for providing multiple beams.

[0013] In another aspect, the invention provides for an improvedinspection method and system in which a scan pattern is notperpendicular to the direction of movement of the wafer.

[0014] In another aspect, the invention provides for an improvedinspection method and system in which a confocal arrangement is used.

[0015] In other aspects, various combinations of the foregoing featuresprovide for improved inspection methods and systems having objects andadvantages that will be more fully appreciated after considering thenon-limiting exemplary embodiments presented below in the detaileddescription, taken together with the enclosed drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The enclosed drawing figures are for the sake of explanationonly, and are not meant to be limiting to the scope of the invention.The drawings are presented in highly simplified form. It will beappreciated that the drawings freely omit elements which, althoughactually necessary for a concrete realization of an actual apparatus,are well understood by those familiar with this field; the omission ofsuch routine elements thus serves to focus attention on the key pointsin the description and avoids obscuring the description with unnecessarydetail. The enclosed drawings are briefly described as follows:

[0017]FIG. 1 shows a semiconductor wafer.

[0018]FIG. 2 shows dies of the semiconductor wafer.

[0019]FIG. 3 shows a laser beam being scanned on a die.

[0020]FIG. 4 shows an inspection apparatus that uses dark field imaging.

[0021]FIG. 5 shows an inspection apparatus that uses bright fieldimaging.

[0022]FIG. 6A shows a pupil of an objective lens when a laser beamhaving a circular shape is used.

[0023]FIG. 6B shows a side view of the objective lens when the laserbeam having the circular shape is used.

[0024]FIG. 7A shows a pupil of an objective lens when a laser beamhaving a ring, or annular, shape is used according to an aspect of theinvention.

[0025]FIG. 7B shows a side view of the objective lens when the laserbeam having the annular shape is used.

[0026]FIG. 7C shows a side view of a conic prism pair suitable forproducing a laser beam having an annular shape.

[0027]FIG. 7D shows the annular beam profile.

[0028]FIG. 7E shows the annular focused beam profile.

[0029]FIG. 8 shows an inspection apparatus according to an aspect of theinvention, in which a laser beam such as that shown in FIG. 6A is used.

[0030]FIG. 9 shows the inspection apparatus as in FIG. 8, in which alaser beam such as that shown in FIG. 6B is used.

[0031]FIG. 10 shows a conventional inspection apparatus for inspecting awafer by using multiple beams.

[0032]FIG. 11 shows a conventional optical apparatus for producingmultiple laser beams from a single incident laser beam.

[0033]FIG. 12 shows an inspection apparatus for inspecting a wafer byusing multiple beams produced according to an aspect of the invention.

[0034]FIG. 13 shows an optical apparatus for producing multiple laserbeams from a single incident laser beam, according to an aspect of theinvention.

[0035]FIG. 14 shows an optical apparatus as in FIG. 13, in which a laserbeam is in a different position from that shown in FIG. 13.

[0036]FIG. 15 shows an exemplary CCD camera for collection, according toone embodiment of the invention.

[0037]FIG. 16A shows a scan pattern for a laser beam in which the scanpattern is perpendicular to the direction of movement of the wafer.

[0038]FIG. 16B shows an effective scan pattern corresponding to the scanpattern shown in FIG. 16A.

[0039]FIG. 16C shows how the effective scan pattern of FIG. 16B can berepresented by a die beam trace.

[0040]FIG. 16D shows, in beam trace form, three scans of the scanpattern of FIG. 16A.

[0041]FIG. 17A shows a scan pattern for a laser beam in which the scanpattern is not perpendicular to the direction of movement of the wafer,according to an aspect of the invention.

[0042]FIG. 17B shows, in beam trace form, three scans of the scanpattern of FIG. 18A, according to an embodiment of the invention.

[0043]FIG. 18 shows, in beam trace form, ten scans of a multi beam scanpattern in which the scan pattern is not perpendicular to the directionof movement of the wafer, according to an aspect of the invention.

[0044]FIG. 19 shows an optical inspection system in which a confocalarrangement is used, according to an aspect of the invention.

DETAILED DESCRIPTION

[0045] Various embodiments of the aspects of the invention will now bepresented, and contrasted with conventional approaches. It will beappreciated that the embodiments are merely exemplary, and that many andvarious modifications can be made within the spirit and scope of theinvention. The scope of the invention is thus not restricted to theseexemplary embodiments, but is to be determined based solely on theappended claims.

[0046]FIG. 6A shows the top view of an objective lens pupil. Such anobjective lens might be used to focus a beam of light onto a die of awafer 10. The entire pupil is shaded, and indicated by reference numeral130. The significance of this is to indicate that an incident beam oflight is a circular laser beam (this will be contrasted with the beamshown in FIG. 7A).

[0047]FIG. 6B shows the side view of the objective lens pupil shown inFIG. 6A. The circular laser beam 130 is focused by the objective lens320 to a desired target point on the wafer 10. The light that reflectsoff the target of the wafer 10 is all contained within the area of thepupil into which the incident light was introduced (i.e., the angle ofincidence must equal the angle of reflectance for a reflected particleof light) In this case, the area of the pupil into which the is incidentlight was introduced happens to be the entire area. The scattered lightis all of the light 110 that is not reflected back into the objectivelens 320.

[0048]FIG. 7A shows the top view of the same objective lens pupil. Notall of the entire pupil is shaded, but only an annular part 150. Aninner part 160 is not shaded. The significance of this is to indicatethat the incident beam of light 140 have been reshaped to have anannular profile. This can be implemented by various optical means knownto those skilled in the art of optics. For example it is possible tointroduce an opaque filter in one of the beam pupil along the opticalpath to block the central part of the beam. Alternatively, it can beachieved by using conic prism pair, as shown in FIG. 7C. To put itanother way, the annular laser beam 140 has an annular part 150 thatincludes incident laser light, and an inner part 160 that does notinclude incident laser light.

[0049]FIG. 7B shows the side view of the objective lens pupil shown inFIG. 7A. The annular laser beam 140 is focused by the objective lens 320to a desired target point on the wafer 10. The light that reflects offthe target of the wafer 10 is all contained within the area of the pupilinto which the incident light was introduced. In this case, the area ofthe pupil into which the incident light was introduced is not the entirearea, but is only the annular part 150. Thus, the reflected lightreflects off the target and backup through the objective lens only inpart of the objective lens illuminated by the annular part 150 of theannular laser beam 140. The scattered light is all of the light that isnot reflected, and includes not only the part of the scattered light 110that is scattered away from the objective lens, but also the part of thescattered light 110 that is scattered up into the part of the objectivelens corresponding to the inner part 160 of the annular beam 140.

[0050] By virtue of using the annular beam 140, a very significant partof the scattered light 110 can be detected by collecting the scatteredlight that is scattered up into the part of the objective lens 320corresponding to the inner part 160 of the annular beam. The annularillumination profile (see FIG. 7D) gives high-resolution since thefocused annular beam size is comparable to that obtained with a fullilluminated pupil, as can be seen in FIG. 7E. The additional side lobecan be minimized by optimizing the radii ratio of the illuminated area.Using that, high resolution can be obtained even in dark field imagingoperations.

[0051] In FIG. 8, a light source 250 and optics 260 are capable ofproducing either a circular beam 130 or an annular beam 140. For brightfield imaging operations, the circular beam 130 is produced. For darkfield imaging operations, the annular beam 140 is produced.

[0052] In FIG. 8, for example, bright field imaging operations areunderway. A circular beam 130 is being produced by the light source 250and optics 260. The beam is scanned by the scanner 300. The beam passesthrough the beam splitter 330 and through the objective lens 320.Reflected light 120 reflects back up through the entire area of thepupil of the objective lens 320 and is reflected by the beam splitter330 to be imaged by the detector 430.

[0053] In FIG. 9, for example, dark field imaging operations areunderway. An annular beam 140 is being produced by the light source 250and optics 260. The beam is scanned by the scanner 300. The beam passesthrough the beam splitter 330 and through the objective lens 320.Scattered light 110 passes, in large measure, through the part of thepupil corresponding to the inner area 160 of the annular beam 140. Thescattered light 110 is reflected off the beam splitter 330 to be imagedby the same detector 430.

[0054] Because the size of the central part of the beam, through whichthe scattered light passes, is known it is of course possible to processjust this part of the light that is reflected from the beam splitter tothe detector 430 and to ignore the reflected light that is passing backthrough the outer part (i.e., the part corresponding to the annular part150).

[0055] Because the size of the central part of the beam and the outerpart of the beam are both known, however, it is possible to process justthe part of the light returned in the inner part as dark fielddetection, and just the part of the light passed back through the outerpart as bright field detection. Thus, when an annular beam is used, darkfield detection and also bright field detection can simultaneously beperformed.

[0056] The imaging system according to this aspect of the inventionincludes an illumination system that selectively produces either acircular (usually Gaussian) beam or an annular beam in response to aselection of imaging operations type. That is, if only bright fieldimaging is selected, the illumination system is controlled to produce acircular beam 130; if dark field imaging is selected, the light sourceis controlled to produce an annular beam 140. Finally, it will also beappreciated that the circular beam 130 and the annular beam 140 arescanned and split in an identical manner.

[0057] While describing the foregoing aspect of the invention, in whichan annular beam 140 is advantageously employed, only a single beam hasbeen discussed. As will be recognized by one familiar with this field,this approach is also applicable in a multi-beam system such as thesystem depicted in FIG. 12 and described more fully below.

[0058] Inspection systems are known, in which multiple beams arecreated. One such system, shown in FIG. 10, is described in U.S. Pat.No. 4,797,696 to Allen, issued on Jan. 10, 1989. In such conventionalsystems as shown in FIG. 10, a light source provides a beam of light.The light is split by a multiple beam splitter and then provided to thescanner. The scanner scans the already-split beams of light through theoptics onto the wafer.

[0059]FIG. 11 shows a conventional example of how the multiple beamsplitter itself might be implemented in a concrete sense. Theillustration is also taken from U.S. Pat. No. 4,797,696 to Allen. Thispatent is incorporated herein by reference for its useful backgroundinformation and concrete examples relating to optical inspectionsystems. In FIG. 11, a single beam 501 is caused to impinge uponmultiple beam splitting members 505. The beam is progressively splitinto multiple beams 170. The multiple beams are then scanned, but thescanning of multiple beams is somewhat more complicated than scanning asingle beam.

[0060]FIG. 12 shows an aspect of the invention which provides forsimplified splitting of beams and simplified scanning in a multiple beamsystem. In FIG. 12, a light source 200 provides a beam of light. Thelight is provided to the scanner 300 via optics 210. After the scanner,the light is provided to the multiple beam splitter 550 according to anaspect of the invention. The multiple beams are then caused to impingeon the target area of the wafer 10 via optics 310, and the resultantlight is collected as desired by bright field detector 420 or dark fielddetectors, depending on the type of imaging operation and imagingapparatus being involved. Of course, it is still possible, within thescope of the invention, to use the multiple beam splitter 550 and thenscan the multiple beams.

[0061]FIG. 13 shows the multiple beam splitter 550 in more detail. Inparticular, a single beam 501 is scanned left and right across theDammann grating 560.

[0062] Dammann gratings are well-known to those familiar with optics,although they have never to the knowledge of the inventor been used inoptical inspection systems in the manner being described now. Forfurther background reading, with the reader may refer to the followingtwo articles: H. Dammann and K. Gortler, “High Efficiency in LineMultiple Imaging by Means of Multiple Phase Holograms”, OpticsCommunication, Vol. 3, May, 1971; and “H. Dammann and E. Koltz,“Coherent Optical Generation and Inspection of Two-dimensional PeriodicStructures”, Optica Acta, Vol. 24, 1977. These two documents areincorporated herein by reference for their useful background informationon Dammann gratings.

[0063] A Dammann grating can be computer designed and generated asdesired by the engineer to produce a plurality of beams (“Beam Brush”)from an incident beam, each of the plurality of beams havingsubstantially identical intensity (although not identity of direction).The plurality of beams can be split from the incident beam in a desiredplane.

[0064] In FIG. 13, the multiple beams 170 are produced by the effect ofthe Dammann grating 560 on the incident beam 501. The multiple beams 170are received by the relay 570 and then focused by the objective onto thesame number of scanning spots.

[0065]FIG. 14 shows a subsequent position of the beam 501. Inparticular, the beam 501 has a different incident angle on the Dammanngrating 560 and now the multiple beams 170 are still produced, but alsohave a different outgoing angle perpendicular to the split axis. Still,the multiple beams 170 are in the same orientation with respect to eachother even though they have been tilted laterally. In FIG. 14, βindicates the scan angle. The scan direction is parallel to the Gratinglines.

[0066] It will be appreciated that the system shown in FIGS. 12-14provides for an optical inspection system and method in which themultiple beam splitter is downstream from the scanner. Moreover,according to this aspect of the invention, the multiple beam splitterincludes a Dammann grating for producing multiple beams 170 from asingle incident beam 501. In FIGS. 13 and 14, the incident beam 501scans horizontally. The multiple beams are produced in a vertical line.Thus, the system according to this aspect of the invention provides forthe production of multiple beams in a line perpendicular to the scanningdirection of the light output from the scanner. The result is a highlysimplified system such that the split is done after the scanning.

[0067] The Dammann grating is used here for the sake of example only,and it will be appreciated that the Dammann grating can be generalizedinto other structures not identical to those strictly adhering to thedescription in the two above-identified articles (much development hasoccurred since the 1970's), which may collectively be referred to asdiffractive optical elements having uniform diffraction efficiency(i.e., elements such as gratings that can split the incoming beam into nbeams of substantially identical intensity).

[0068]FIGS. 8 & 9 show basic optical schemes for the collection of thelight. The scanning beam or beams may be imaged onto a line CCD or amulti line CCD. Likewise, the beam or beams may each be focused into aPIN diode or PMT detector.

[0069] In FIG. 15, an exemplary CCD camera has rectangular pixels with arectangular pitch. The pitch size in the vertical (optical scan)direction is m*P where m is the required magnification and P is the sizeof a pixel. The pitch in the horizontal direction (the mechanicalscanning direction in the foregoing examples) is m*D where D is thedistance in between brush lines. The detector cell array should have afill factor as high as possible in the vertical direction, but much lessis required in the horizontal direction. An aspect ratio of 1:5 to 1:10would relax the alignment tolerances of the CCD with respect to theoptical scan direction. The number of pixels k and the number of lines nmay be, for example, 2000 pixels and 35 lines, respectively. It will beappreciated that other values may naturally be used in accordance withthe above principles and the particulars of a given situation. Usingthis type of camera allows for a detector in which each of the severalbeams is received on separate lines of CCD camera.

[0070] Another aspect of the invention will now be described withreference to the FIGS. 16-19.

[0071]FIG. 16A shows a scan pattern for a laser beam in which the scanpattern is perpendicular to the direction of movement of the wafer. Inparticular, the beam spot 100 is scanned by a scanner along a lineindicated by 600. The line indicated by 600 may be thought of as ascanning direction or a scan pattern. The scan pattern shown in 16A is apattern represented as being independent of the wafer on which it isscanned. Another way to think of this, is that the scan pattern is shownas if the wafer were not being moved. In actuality, the wafer isconstantly being moved.

[0072]FIG. 16B is an illustration that takes into account the movementof the wafer. It is well understood that the wafer is moved by the stage12 so that the entire surface of the wafer can be inspected. In thisfigure, 601 represents the initial position of the beam spot 100 at thebeginning of the scan. As a small amount of time progresses, the waferis moved slightly in the mechanical scanning direction M and the beamspot 100 moves in the optical scanning direction 0 to the positionindicated by 602. As the wafer is moved even more, the beam spot 100 ismoved through positions 603 and 604 to the end of the scan pattern atposition 605. After this, the beam spot is instantaneously moved to theposition indicated by 601′.

[0073] It will be appreciated that positions 601 through 605 are notdiscrete positions, but the beam is moved smoothly and continuouslybetween the beginning scan position 601 and the final scan position 605.When the beam is moved from the final scan position 605 to the initialscan position 601′ for the next scan cycle, it is moved discontinuously,and “skips” back to the initial scan position.

[0074] In FIG. 16B, the distance indicated by T represents the distancein between scan lines along the stage movement direction (i.e., in themechanical scanning correction). That is to say, T represents how farthe stage is moved during the time it takes for the scanning beam tomove from the initial scanning position 601 of a present scan cycle tothe initial scanning position 601′ of the next scan cycle.

[0075] The illustrations shown in FIGS. 16A and 16B are two ways ofrepresenting the same physical result. FIG. 16A may be said to show ascan pattern, while FIG. 16B may be said to show an effective scanpattern. Thus, the effective scan pattern is a representation that takesinto account the movement of the wafer in the mechanical scanningdirection.

[0076] Another way to represent the effective scan pattern is shown inFIG. 16C. Here, a solid line 610 shows the movement of the center of thebeam spot starting at the initial scan position and moving through thefinal scan position. A line of dashes 615 between the final scanposition and the initial scan position of the next scan cycle representsthe jump of the beam spot to move into position for the next scan cycle.The line 610 may be referred to as the effective scan line, and the line615 may be referred to as the effective return scan line.

[0077]FIG. 16D shows, in beam trace form, three scans of the scanpattern of FIG. 16A. Although the scan pattern shown in FIG. 16A has ascan direction 600 that is perpendicular to the mechanical scanningdirection M, it is apparent that the effective scan pattern is such thatthe initial position for the next scan cycle 601′ is below the finalscan position 605 of the previous scan cycle. In other words, thedistance, in the mechanical scanning direction M, traveled by the beamduring the scan cycle is substantially equal to T (how far the stage ismoved during the time it takes for the scanning beam to move from theinitial scanning position 601 of a present scan cycle to the initialscanning position 601′ of the next scan cycle).

[0078]FIG. 17A shows a scan pattern for a laser beam in which the scanpattern is not perpendicular to the direction of movement of the wafer,according to an aspect of the invention. In particular, the scan patternfor the beam spot 100 includes a scan direction 650.

[0079] In FIG. 17B, M represents the direction of movement of the wafer(i.e., the mechanical scanning direction). D represents the distance inbetween the brush lines. T represents the distance in between scan linesin the mechanical scanning direction. FIG. 17B shows, in beam traceform, three scans of the scan pattern of FIG. 17A, with 660 representingthe effective scan line and 665 representing the scan return scan line.Because the scan direction 650 is not perpendicular to the mechanicalscanning direction, the beam spot travels a distance in the mechanicalscanning direction that is always greater than T. In both FIGS. 17b and18, M′ represents a reference line that is in the same direction as themechanical scanning direction, and is shown to make clear the existenceof an angle α. This angle a may be referred to as the scan line tiltangle. P represents the distance between scan lines, and thus the pixelsize.

[0080]FIG. 18 shows, in beam trace form, ten scans of a multi beam scanpattern with a beam brush of n=4 in which the scan pattern is notperpendicular to the direction of movement of the wafer. In FIG. 18, Mrepresents the direction of movement of the wafer (i.e., the mechanicalscanning correction). D represents the distance in between the brushlines. T represents the distance in between scan lines in the mechanicalscanning direction. HFOV represents the number of pixels in thehorizontal field of view. NPL represents the number of pixels along thescan line.

[0081] Because the beam spot travels a distance in the mechanicalscanning direction that is greater than T, a very accurate die-to-diecomparison can be obtained, with increased assurance that the same linehas scanned the same place on the two different dies being compared. Ofcourse, it goes without saying that the comparison between the twodifferent dies must be made at different times in order for the sameline to scan the same place on the two different dies. The data can bebuffered in a manner well-known to those familiar with this field, andstored in a memory as necessary until the comparison can be made.

[0082] From the foregoing, and as can be seen from FIG. 18, therelations shown below follow directly (assuming that τ is the amount oftime it takes for the stage to move the distance T) and can be used todetermine the stage velocity and data rate: $\begin{matrix}{D = {{\frac{HFOV}{n - 1}\quad \ldots \quad {where}\quad n} > 1}} & \left( {{Equation}\quad 1} \right) \\{{\sin \quad \alpha} = {\frac{D}{NPL} = \frac{HFOV}{\left( {n - 1} \right) \cdot {NPL}}}} & \left( {{Equation}\quad 2} \right) \\{T = {\frac{P}{\sin \quad \alpha} = {\frac{P}{\left( \frac{HFOV}{\left( {n - 1} \right) \cdot {NPL}} \right)} = \frac{P \cdot \left( {n - 1} \right) \cdot {NPL}}{HFOV}}}} & \left( {{Equation}\quad 3} \right) \\{{DR} = \frac{n \cdot {NPL}}{\tau}} & \left( {{Equation}\quad 4} \right)\end{matrix}$

[0083] where

[0084] n=number of beams

[0085] P=pixel size

[0086] HFOV=number of pixels in horizontal field of view

[0087] NPL=number of pixels along the scan line

[0088] DR=data rate in pixels per second

[0089] D=distance in between brush lines

[0090] T=distance in between scan lines in the stage movement direction

[0091] τ=the scan line time

[0092] α=the scan line tile angle.

[0093]FIG. 19 shows another aspect of the invention, in which in which aconfocal arrangement is used for optical focus.

[0094] In FIG. 19, a light source 900 provides light through a beamshaper 905. The beam shaper provides the light through the pupil 907 andthe multiple beam splitter 908 (which may be a Dammann grating). Themultiple beams are provided to a beam splitter 910 and then throughscanning means 915, 920. The scanner outputs light to a relay 925 and abeam splitter 930. The beam splitter 930 illuminates a target on wafer945 through first objective lens 940 using magnification telescope 935.

[0095] Light returned back from the illuminated spot on the specimen,collected by the objective 940, passes back through the scan unit inorder to cancel the optical scanning, so that the returning beams willbe static upon the detectors. Then the reflected beams, which may bethought of as a returned light signal, are deflected by beam splitter910 towards a focusing lens 912. The lens 912 focuses all the beams to apinhole 913 in order to obtain the confocal effect. After passing thepinhole each beam is collected (by means of additional optical means,not shown, but readily implemented by one familiar with this field) ontoa respective independent detector 914. This confocal pinhole 913 (whichmay be referred to as a confocal optical element) is what gives thesystem its confocal property, by rejecting light that did not originatefrom the focal plane of the microscope objective. Light rays from belowthe focal plane come to a focus before reaching the detector pinhole,and then they expand out so that most of the rays are physically blockedfrom reaching the detector by the detector pinhole.

[0096] In the same way, light reflected from above the focal planefocuses behind the detector pinhole, so that most of that light alsohits the edges of the pinhole and is prevented from reaching thedetector 914. However, all the light from the focal plane is focused atthe detector pinhole in blocking member 913 and so is detected at thedetector 914.

[0097] Because of the confocal arrangement, the depth of focus of theinspection apparatus is greatly narrowed, making it possible to suppressthe signals from the under-layers. The signals from the under-layers inmost cases are not important and introduce noise to the image processingsystem. Also it is possible to use the confocal arrangement togetherwith annular illumination mode in order to suppress DF signals fromunder layers.

[0098] For the sake of completeness, it will be mentioned that theimaging light reflected from the wafer 945 passes up through the beamsplitter 930 and through imaging lens 950 to another beam splitter 955.In this exemplary arrangement, the bright field channel light iscollected by CCD camera 960. The dark field channel light is collectedby a CCD or PMT 965.

[0099] In another aspect of the invention, an optical inspection systemmay include various combinations of the foregoing other aspects. Forexample, the use of an annular beam for dark field/bright fieldoperations may be combined with a multiple beam brush created using adiffractive optical element having uniform diffraction efficiency, andmay be combined with a system in which the scan direction is notperpendicular to the mechanical scanning direction, and may be combinedwith a system having a confocal focus arrangement. Likewise, thecreation of multiple beams using a diffractive optical element havinguniform diffraction efficiency may be combined with a system in whichthe scan direction is not perpendicular to the mechanical scanningdirection, and may be combined with a system having a confocal focusarrangement. Likewise, a system in which the scan direction is notperpendicular to the mechanical scanning direction may be combined witha system having a confocal focus arrangement. Finally, combinations ofany or all of the aspects of the invention are also possible.

[0100] As mentioned above, the exemplary embodiments shown in thefigures and described above are for the sake of explanation and are notmeant to be limiting upon the invention. Many specificities have beenmentioned, but these are also not meant to be limiting on the invention.Rather, the scope of the invention is to be interpreted in accordancewith the spirit of the invention, in accordance with the claims below.

What is claimed is:
 1. An optical inspection system, comprising: a lightsource outputting an annular beam; an objective lens focusing theannular beam at a target; and a detector receiving light scattered fromthe target, through the objective lens.
 2. The optical inspection systemas set forth in claim 1, wherein: the light source also outputs acircular beam; the objective lens focuses the circular beam at thetarget; and the detector receives light reflected from the targetthrough the objective lens.
 3. The optical inspection system as setforth in claim 2, wherein the light source produces a selected one ofthe annular beam and the circular beam in response to a selection ofimaging operation type.
 4. The optical inspection system as set forth inclaim 3, wherein, when the imaging operation type is bright fieldimaging, the light source is controlled to produce the circular beam,and, when the image operation type is dark field imaging, the lightsource is controlled to produce the annular beam.
 5. The opticalinspection system as set forth in claim 1, wherein: the detectorreceives the scattered light, as dark field detection, through a portionof the objective lens corresponding to an inner part of the annularbeam; and the detector simultaneously receives light reflected from thetarget, as bright field detection, through a portion of the objectivelens corresponding to an outer part of the annular beam.
 6. The opticalinspection system as set forth in claim 1, further comprising: a scannerscanning the annular beam along a line in a given scanning direction toprovide a scanned single annular beam; and a multiple beam splitterproducing multiple annular beams of substantially identical intensityfrom the scanned single annular beam.
 7. The optical inspection systemas set forth in claim 6, wherein: the detector receives the scatteredlight, as dark field detection, through a portion of the objective lenscorresponding to an inner part of each of the annular beams; and thedetector simultaneously receives light reflected from the target, asbright field detection, through a portion of the objective lenscorresponding to an outer part of each of the annular beams.
 8. Theoptical inspection system as set forth in claim 6, wherein the detectoris a multiple line CCD camera, and wherein each of the multiple annularbeams is imaged on a separate one of the lines of the multiple line CCDcamera.
 9. An optical inspection system, comprising: a light sourceoutputting a single beam; a scanner scanning the single beam along aline in a given scanning direction to provide a scanned single beam; anda multiple beam splitter producing multiple beams of substantiallyidentical intensity from the scanned single beam.
 10. The opticalinspection system as set forth in claim 9, wherein the multiple beamsplitter produces the multiple beams with a diffractive optical elementhaving uniform diffraction efficiency.
 11. The optical inspection systemas set forth in claim 10, wherein the diffractive optical element is aDammann grating.
 12. The optical inspection system as set forth in claim9, further comprising: an objective lens focusing the multiple beams ata target; and a detector receiving light returned from the target,through the objective lens wherein the detector includes a multiple lineCCD camera, and wherein each of the multiple annular beams is receivedon a separate one of the lines of the multiple line CCD camera.
 13. Anoptical inspection system, comprising: a light source outputting a beam;and a scanner scanning the beam in a beam spot across a target, thetarget being movable in a target movement direction; wherein the beamhas a scanning direction not perpendicular to the target movementdirection.
 14. The optical inspection system as set forth in claim 13,wherein the beam spot travels a distance in the mechanical scanningdirection that is greater than the distance in between scan lines in themechanical scanning direction.
 15. An optical inspection system,comprising: a light source outputting a beam; a confocal opticalarrangement; and optics for focusing the beam at a target and directingcaptured light to a detector through the confocal optical arrangement.16. The optical inspection system as set forth in claim 15, furthercomprising a control unit controlling the focus of the optics based on:a light level threshold, and a light level signal indicative of lightreceived by the detector through the confocal optical arrangement.
 17. Amethod for optical inspection, comprising: generating an annular lightbeam; scanning the annular beam along a line in a given scanningdirection to provide a scanned single beam; and splitting the scannedsingle beam to provide multiple beams of substantially identicalintensity from the scanned single beam; and detecting signals generatedfrom an interaction between the plurality of multiple beams and aninspected object.
 18. An optical inspection system, comprising: a lightsource providing a beam of light through a pupil; a multiple beamsplitter receiving the light through the pupil; a scanner receiving themultiple beams and providing scanned multiple beams; a beam splitterreceiving the scanned multiple beams and illuminating a target throughan objective lens; the objective lens collecting light returned backfrom the illuminated target and passing the collected light through thebeam splitter to an imaging lens; the imaging lens receiving the lightpassing through the beam splitter and focusing the light to a brightfield channel detector.
 19. The optical inspection system as set forthin claim 18, wherein the bright field channel detector includes amultiple line CCD camera, and wherein each of the multiple annular beamsis received on a separate one of the lines of the multiple line CCDcamera.
 20. The optical inspection system as set forth in claim 18,further comprising: an other beam splitter optically disposed betweenthe imaging lens and the bright field channel detector; and the lightfrom the imaging lens passing through the beam splitter being focusedalso on a dark field channel detector.
 21. The optical inspection systemas set forth in claim 20, wherein at least one of the bright fieldchannel detector and the dark field channel detector includes a multipleline CCD camera, and wherein each of the multiple annular beams isreceived on a separate one of the lines of the multiple line CCD camera.22. An optical inspection system, comprising: a light source providing abeam of light; a scanner receiving the light through a first beamsplitter and providing scanned light; a second beam splitter receivingthe scanned light through a scan lens, and illuminating a target throughan objective lens; the objective lens collecting light returned backfrom the illuminated target and passing the collected light to thesecond beam splitter; the second beam splitter providing part of thecollected light, as a returned light signal, back through the scan lensand scanner to the first beam splitter; the first beam splitterdeflecting the returned light signal through a focusing lens and apinhole; and one or more detectors receiving the light through thepinhole.
 23. The optical inspection system as set forth in claim 22,wherein: the light source provides the beam of light through a pupil; amultiple beam splitter receives the light through the pupil; the lightreceived by the scanner includes multiple beams provided by the multiplebeam splitter, and the light scanned by the scanner includes multiplescanned beams; the second beam splitter provides part of the collectedlight through an imaging lens to a bright field channel detector. 24.The optical inspection system as set forth in claim 23, wherein thebright field channel detector includes a multiple line CCD camera, andwherein each of the multiple annular beams is received on a separate oneof the lines of the multiple line CCD camera.
 25. The optical inspectionsystem as set forth in claim 23, further comprising: a third beamsplitter optically disposed between the imaging lens and the brightfield channel detector; and the light from the imaging lens passingthrough the third beam splitter being focused also on a dark fieldchannel detector.
 26. The optical inspection system as set forth inclaim 25, wherein the multiple scanned beams are annular beams.
 27. Theoptical inspection system as set forth in claim 25, wherein at least oneof the bright field channel detector and the dark field channel detectorincludes a multiple line CCD camera, and wherein each of the multipleannular beams is received on a separate one of the lines of the multipleline CCD camera.
 28. The optical inspection system as set forth in claim23, wherein the multiple beam splitter produces the multiple beams witha diffractive optical element having uniform diffraction efficiency. 29.The optical inspection system as set forth in claim 28, wherein thediffractive optical element is a Dammann grating.
 30. The opticalinspection system as set forth in claim 22, wherein: the target ismovable in a target movement direction; and the scanner scans with ascanning direction not perpendicular to the target movement direction.31. An optical inspection method, comprising: outputting an annular beamfrom a light source; focusing the annular beam at a target; anddetecting light scattered from the target.
 32. The optical inspectionmethod as set forth in claim 31, further comprising: outputting acircular beam from the light source; focusing the circular beam at thetarget; and detecting light reflected from the target.
 33. The opticalinspection method as set forth in claim 32, further comprising:selecting an imaging operation type; producing a selected one of theannular beam and the circular beam in based on the imaging operationtype.
 34. The optical inspection method as set forth in claim 33,wherein, when the imaging operation type is bright field imaging, thelight source is controlled to produce the circular beam, and, when theimage operation type is dark field imaging, the light source iscontrolled to produce the annular beam.
 35. The optical inspectionmethod as set forth in claim 31, wherein: the detecting of the scatteredlight detects the light scattered through a portion of an objective lenscorresponding to an inner part of the annular beam; and simultaneouslywith the detecting of the scattered light there is a detection of lightreflected from the target, as bright field detection, through a portionof the objective lens corresponding to an outer part of the annularbeam.
 36. The optical inspection method as set forth in claim 31,further comprising: scanning the annular beam along a line in a givenscanning direction to provide a scanned single annular beam; andproducing multiple annular beams of substantially identical intensityfrom the scanned single annular beam.
 37. The optical inspection methodas set forth in claim 36, wherein: the detecting of the scattered lightdetects the light scattered through a portion of an objective lenscorresponding to an inner part of each of the annular beams; andsimultaneously with the detecting of the scattered light there is adetection of light reflected from the target, as bright field detection,through a portion of the objective lens corresponding to an outer partof each of the annular beams.
 38. The optical inspection method as setforth in claim 36, wherein the detecting is performed with a multipleline CCD camera, and includes imaging each of the multiple annular beamson a separate one of the lines of the multiple line CCD camera.
 39. Anoptical inspection method, comprising: outputting a single beam;scanning the single beam along a line in a given scanning direction toprovide a scanned single beam; and producing multiple beams ofsubstantially identical intensity from the scanned single beam.
 40. Theoptical inspection method as set forth in claim 39, wherein theproducing of the multiple beams is performed with a diffractive opticalelement having uniform diffraction efficiency.
 41. The opticalinspection method as set forth in claim 40, wherein the diffractiveoptical element is a Dammann grating.
 42. The optical inspection methodas set forth in claim 39, further comprising: focusing the multiplebeams at a target through an objective lens; receiving light returnedfrom the target, through the objective lens; and detecting the returnedlight with a multiple line CCD camera by imaging each of the multipleannular beams on a separate one of the lines of the multiple line CCDcamera.
 43. An optical inspection method, comprising: outputting a beam;and scanning the beam in a beam spot across a target, the target beingmovable in a target movement direction; wherein the beam has a scanningdirection not perpendicular to the target movement direction.
 44. Theoptical inspection method as set forth in claim 43, wherein the beamspot travels a distance in the mechanical scanning direction that isgreater than the distance in between scan lines in the mechanicalscanning direction.
 45. An optical inspection method, comprising:outputting a beam; and focusing the beam at a target; and directingcaptured light to a detector through a confocal optical arrangement. 46.The optical inspection method as set forth in claim 45, furthercomprising controlling the focus of the optics based on: a light levelthreshold, and a light level signal indicative of light received by thedetector through the confocal optical arrangement.
 47. An opticalinspection method, comprising: providing a beam of light; providingscanned multiple beams from the beam of light; illuminating a target,with the scanned multiple beams, through an objective lens; collectinglight, returned back from the illuminated target, with the objectivelens; passing the collected light through to an imaging lens; focusingthe light of the imaging lens to a bright field channel detector. 48.The optical inspection method as set forth in claim 47, wherein thebright field channel detector includes a multiple line CCD camera, andwherein each of the multiple annular beams is received on a separate oneof the lines of the multiple line CCD camera.
 49. The optical inspectionmethod as set forth in claim 47, further comprising: providing a beamsplitter optically disposed between the imaging lens and the brightfield channel detector; and focusing a portion of the light, from theimaging lens, through the beam splitter and also on a dark field channeldetector.
 50. The optical inspection method as set forth in claim 49,wherein at least one of the bright field channel detector and the darkfield channel detector includes a multiple line CCD camera, and whereineach of the multiple annular beams is received on a separate one of thelines of the multiple line CCD camera.
 51. An optical inspection method,comprising: providing a beam of light; passing the beam of light througha first beam splitter; scanning the light received through a first beamsplitter to provide scanned light; passing the scanned light through ascan lens and a second beam splitter, and illuminating a target throughan objective lens; collecting light returned back from the illuminatedtarget; passing the collected light to the second beam splitter;providing part of the collected light, as a returned light signal, backthrough the scan lens and scanner to the first beam splitter; deflectingthe returned light signal, with the first beam splitter, through afocusing lens and a pinhole; and receiving the light through the pinholeusing one or more detectors.
 52. The optical inspection method as setforth in claim 51, further comprising: providing the beam of light, fromthe light source, through a pupil; receiving the light through the pupilat a multiple beam splitter; splitting the beam of light using themultiple beam splitter; providing the scanned light as multiple scannedbeams; providing part of the collected light, from the second beamsplitter, through an imaging lens to a bright field channel detector.53. The optical inspection method as set forth in claim 52, wherein thebright field channel detector includes a multiple line CCD camera, andwherein each of the multiple annular beams is received on a separate oneof the lines of the multiple line CCD camera.
 54. The optical inspectionmethod as set forth in claim 52, further comprising: providing a thirdbeam splitter optically disposed between the imaging lens and the brightfield channel detector; and focusing the light from the imaging lensthrough the third beam splitter also onto a dark field channel detector.55. The optical inspection method as set forth in claim 54, wherein themultiple scanned beams are provided as annular beams.
 56. The opticalinspection method as set forth in claim 54, wherein at least one of thebright field channel detector and the dark field channel detectorincludes a multiple line CCD camera, and wherein each of the multipleannular beams is received on a separate one of the lines of the multipleline CCD camera.
 57. The optical inspection method as set forth in claim52, wherein the multiple beam splitter is a diffractive optical elementhaving uniform diffraction efficiency.
 58. The optical inspection methodas set forth in claim 57, wherein the diffractive optical element is aDammann grating.
 59. The optical inspection method as set forth in claim51, wherein: the target is movable in a target movement direction; andthe scanner scans with a scanning direction not perpendicular to thetarget movement direction.